Hi, i had an issue that after some time only the TEMPDB was monitored for my clustered instances. I had no clue why and after some internetting i found removing and re-adding them to the system was an option. After doing this the cluster add's the nodes (hosts) but only attempts to connect to the 'local' instance. the other instances are no longer listed...

Which version of SQL Monitor are you using? We changed the behaviour of how cluster is added in v3.2. V3.2 onwards if you try to add a cluster using the node names then it will only add that node and instances local to it. To add cluster, you would have to use the cluster management node address.

Can you try adding the cluster using Cluster management node address rather than one of the nodes and let us know if that works for you?